In the manufacture of corrugated boxes and other corrugated goods, a large sheet of corrugated fiberboard is passed through a machine which will die cut the blank or flat shape of corrugated boxes or other objects which are to be constructed from the sheet of corrugated fiberboard. The sheets of corrugated fiberboard may be die cut in a press which acts in the manner of a die cutting machine to stamp the pattern of the blank into the fiberboard. Alternately, the sheet of fiberboard may pass through a rotary die which will cut and emboss the blank pattern of the final shape of the knock-down carton or the like to be made from the sheet.
To simplify handling of the corrugated material, the die cut blanks are not separated completely from the sheet, but are left partially joined along adjacent edges which will separate under tension to produce the individual blanks for later formation into cartons, boxes, or other objects. This allows for simplified handling in that the process only needs to handle complete sheets rather than all of the individual blanks. Since several blanks may be separated from a single sheet, there is an increase in efficiency from handling a single sheet versus a multitude of blanks cut from the sheet.
However, at some point the blanks defined by the rotary press or the platen die press will need to be separated so that they may be individually bundled and shipped or further processed into finished goods. In the manufacture of corrugated goods it is desirable to remove as many bottlenecks from the process as possible by minimizing handling steps. It is therefore desirable to separate the blanks from the primary sheet or sheets in a minimal number of steps.
One method to minimize the number of handling steps is to collect several sheets into a stack and then separate the stack into bundles of blanks. The more sheets in a stack of corrugated fiberboard which can be handled at one time, the more efficient the process will be. However, as more sheets are accumulated into a stack to increase throughput, a larger force will be required to separate a stack of fiberboard along the defined separation line.
Some die cutting processes will cut away portions of the corrugated sheet along a line defining the separation path of the blank to be separated from the fiberboard. In the cut away area, small tabs will be left so the blank does not separate from the primary sheet. The small tabs are termed "nicks" and a sheet with die-cut blanks held in place by nicks is termed a "nicked sheet." Alternately, the die may impress a crease along the fiberboard or partially cut through the fiberboard to define the separation path. Either of these processes will create an area of weakened tensile strength such that when the fiberboard is subjected to a tensile force acting in the plane of the sheet, the sheet will tear or separate along the defined separation path. Since a multitude of separation paths may be imposed into a single sheet of fiberboard, it is necessary to impose the tensile strength required to separate the sheet along a selected separation line, rather than subjecting the entire sheet to tensile strength with resultant random separation along the separation lines.
One method for separating a bundle of blanks from a stack of nicked sheets consists of grasping the stack of corrugated sheets along either side of a plane of separation paths passing through the stack of sheets and then pulling the two grasped portions apart to sever the bundle from the remaining stack. As the stacks become higher to increase the rate of through put, more tensile force is required to separate the bundle from the stack. In order to achieve greater tension forces, larger grasping or clamping forces must be applied to the stack. At a certain point, the compressive forces applied by the clamps on either side of the separation path become so high that the fiberboard is damaged by the clamps. On the other hand, too little clamping force will result in the fiberboard slipping from the clamps during the pulling process.
It is therefore desirable to produce a apparatus for separating bundles of blanks from a stack of nicked sheets having such blanks die cut within the individual sheets, which allows for large stacks of sheets to be processed without damaging the sheets themselves in the process.